If tracer modifies a syscall number to -1, this traced system call should be skipped with a return value specified in x0. This patch implements this semantics.
Please note: * syscall entry tracing and syscall exit tracing (ftrace tracepoint and audit) are always executed, if enabled, even when skipping a system call (that is, -1). In this way, we can avoid a potential bug where audit_syscall_entry() might be called without audit_syscall_exit() at the previous system call being called, that would cause OOPs in audit_syscall_entry().
Signed-off-by: AKASHI Takahiro takahiro.akashi@linaro.org --- arch/arm64/kernel/entry.S | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 726b910..5d6a399 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -668,8 +668,15 @@ ENDPROC(el0_svc) * switches, and waiting for our parent to respond. */ __sys_trace: - mov x0, sp + mov w0, #-1 // set default errno for + cmp scno, x0 // user-issued syscall(-1) + b.ne 1f + mov x0, #-ENOSYS + str x0, [sp, #S_X0] +1: mov x0, sp bl syscall_trace_enter + cmp w0, #-1 // skip the syscall? + b.eq __sys_trace_return_skipped adr lr, __sys_trace_return // return address uxtw scno, w0 // syscall number (possibly new) mov x1, sp // pointer to regs @@ -683,7 +690,8 @@ __sys_trace: br x16 // call sys_* routine
__sys_trace_return: - str x0, [sp] // save returned x0 + str x0, [sp, #S_X0] // save returned x0 +__sys_trace_return_skipped: mov x0, sp bl syscall_trace_exit b ret_to_user